Timing circuit



June 18, 195? M. c. HOOVER ETAL TIMING CIRCUIT Filed Sept. 21, 1954 INVENTORS MICHAEZL c. uoovee cmvrom VANDEE MEER ATTORNEYS United States Patent P TIMING CIRCUIT Michael C. Hoover and Clayton H. Vander Meer, Grand Rapids, Mich., assignors to Mandrel industries, inc, a corporation of Michigan Application September 21, 1954, genial No. 457,492

Claims. (Cl. 307-132) This invention relates to electrical timing and pertains particularly to timing circuits.

It is an object of our invention to provide a timer capable of producing a pulse which may be varied in duration within wide limits and which may be repeated auto matically at relatively long time intervals.

It is an object of the invention to provide adjustability over a wide range in the interval between pulses as well as in the duration of each pulse.

A further object of our invention is to provide accurate control of pulse duration as well as pulse interval.

It is an object of our invention to provide a relatively simple mechanical apparatus and simple electrical circuits for accomplishing a high degree of accuracy and a wide range of adjustability.

Still another object of the invention is to enable pulse duration to be determined solely by electrical-circuit constants especially resistance and capacity.

Other and further object, features and advantages of the invention will become apparent as the description proceeds.

In carrying out the invention in accordance with a preferred form thereof, a synchronous motor is provided for driving a cam switch to ignite an ionic-discharge type of electrical discharge device intermittently. A discharge tube is employed of the type having a control electrode which ignites the tube when the control voltage is raised above a predetermined value, but leaves the continuity of current-flow unaffected when the control voltage falls. An alternating-current source is provided for supplying the electric discharge device so that it de-ionizes upon reversal of voltage whenever the control grid potential is below a predetermined value. For controlling the duration of the pulse, a resistance-capacity circuit is provided which reduces the potential of the control electrode at a rate dependent upon the resistance and capacity constants.

A better understanding of the invention will be aiforded by the following detailed description considered in conjunction with the accompanying drawing which constitutes a schematic circuit diagram of an embodiment of the invention.

Referring to the drawing, there is a synchronous motor 11 energized by a source of alternating current 12, a drive shaft 13, and a double throw cam switch 14, which is driven by the shaft 13 through a gear rack 15 of interchangeable gears 16 and 17.

The cam switch 14 is preferably of the snap action type. For simplicity in the drawing it is represented schematically as consisting of a cam 18 driven by the gear 17, a cam follower or switch button 19 actuated by the cam 18, and a pair of alternative stationary contacts 21 and 22 and a movable contact 23 secured to the cam follower 19. The movable contact 23 is arranged to make contact with a conductor 24 in either extreme position of the movable contact 23. As shown in the schematic illustration, the movable contact 23 is adapted to cooperate with fixed contacts 25 and 26 both connected to the conductor 24.

An electric discharge device or ionic discharge device masses Patented June 18, 1957 ICC 27 of the gas or vapor filled type, referred to herein as a thyratron, is provided for pulsing the flow of current through a relay 2801' other device in which current pulses are to be produced of accurately determined duration at fixed relatively long intervals. The thyratron 27 has an anode 29, cathode 31 and control electrode or grid 32. The anode 29 and the cathode 31 are connected in series with the relay 28 to the alternating-current supply terminals 12.

A source of direct current is also provided, having a positive terminal 33 and a negative terminal 34. The positive terminal 33 is connected to the stationary contact 21 of the cam switch 14 and the negative terminal 34 is connected to the junction of resistors 36 and 39. An intermediate point 40 of the source 30 is grounded for pro vidi-ng negative bias for the thyratron 27.

For fixing pulse duration, a condenser and resistor 36, having a junction terminal 37, are connected in series between the conductor 24 and the negative terminal 34, the condenser 35 being connected to the conductor 24. The junction terminal 37 is connected to the control electrode 32 of the thyratron 37 through a current limiting resistor 38.

A discharge resistor 39 is also provided, which is connected between the stationary contact 22 of the cam switch 14 and the negative terminal 34. To avoid chattering of the relay 28, a condenser 41 is preferably connected across its actuating coil.

The interval between pulses or operations of the relay 28 is determined by the selection of gears 16 and 17 used in the gear rack 15 and by the speed of the shaft 13, driven by the synchronous motor 11. Further variation may be accomplished by substituting synchronous motors with different numbers of poles or providing a pole-changing switch.

Whenever the cam 13 is rotated to the position illustrated, the contact 21 closes and a circuit is formed from the positive terminal 33 of the direct-current source,

rent source.

through the contacts 21, 23, conductor 24, condenser 35, resistor 36 to the negative terminal 34 of the direct-cur- The surge of charging current through the condenser 35 produces a voltage drop in the resistor 36 raising the potential of the junction terminal 37 connected to the thyratron grid 32.

' Accordingly the thyratron 27 is ionized and current begins to flow from the source 12 through the relay 28 and the thyratron 27. As charging current continues to flow through the condenser 35, however, the potential difference between its plates gradually rises until the flow of current ceases. The potential of the junction terminal 37 as well as that of the thyratron grid 32 falls to the negative potential of the terminal 34 of the direct-current source. Since the anode supply for the thyratron 27 is alternating current, as soon as the potential of the grid 32 has fallen to the critical value, which is approximately the potential of the cathode 31, depending upon the design of the thyratron used, the how of current through thyratron 27 is interrupted and the current pulse through the relay 28 is terminated.

The duration of the pulse depends entirely upon the constants of the elements 35 and 36 assuming constant supply voltage. Since the apparatus is connected to a constant-voltage system, the practical criterion of pulse length is the electrical time constants of the circuit elements 35 and 36. Pulse length may, therefore, readily be changed over wide ranges by substitution of a resistor or condenser of different value. These elements may be of the plug in type or variable elements may be employed.

As the cam 18 continues to rotate, the cam follower 19 will come to the steep descending portion 42, whereupon the movable contact 23 will close the contact 32. A discharge circuit for the condenser 35 is then formed through the conductor 24, the fixed terminal 26, the mova able contact 23, the stationary contact 22, a conductor 43, the resistors 39 and 36 back to the junction terminal 37 of the condenser 35. The resistor 39 serves to limit the condenser discharge current to a safe value. The condenser 41 causes current to continue flowing in the relay 28 for the duration of the pulse and thus overcomes chatter.

Owing to the provision for interchangeability of mechanical parts and electrical elements, the pulse duration may readily be varied within such wide limits as from of a second to 30 seconds, for example. The time between pulses can be varied from approximately seconds to 72 hours or more.

In accordance with the provisions of the patent statutes, the principle of operation of the invention has been described together with the apparatus now believed to represent the best embodiment thereof, but it is to be understood that the apparatus shown and described is only illustrative and that the invention may be carried out by other arrangements.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A timing system comprising in combination a synchronous motor, a pair of terminals for connection to a source of alternating current, an interchangeable gear rack, a double-throw switch having two stationary contacts and a movable contact and an operating cam rotated by said motor through said rack, a thyratron having a control electrode, and having an anode and a cathode in a circuit connected to said alternating-current terminals, a relay having a winding in series with the thyratron, a condenser shunting said winding, a pair of terminals for connection to a source of direct current, one connected to the cathode of said thyratron, the other connected to one of the stationary contacts of said cam switch, a timing resistor connected at one end to said cathode, a timing condenser connected between said resistor and the movable cam switch contact, a current-limiting resistor connected between the control electrode of said thyratron and the junction of the timing resistor and condenser, and a discharge resistor connected between the said cathode and the remaining stationary cam-switch contact.

2. A timing system comprising in combination a constant speed motor, a pair of terminals for connection to a source of alternating current, an interchangeable gear rack, a switch having two contacts and an operating cam, rotated by said motor through said rack, a thyratron having a control electrode and having an anode and a cathode in a circuit connected to said alternating-current terminals, a relay having a winding in series with the thyratron, a pair of terminals for connection to a source of directcurrent, one connected to the cathode of said thyratron, the other connected to one of said contacts of said cam switch, a timing resistor connected at one end to said cathode, a timing condenser connected between said resistor and the remaining cam switch contact, and a connection between the thyratron control electrode and the junction of the resistor and the condenser.

3. A timing system comprising in combination a synchronous motor, a pair of terminals for connection to a source of alternating current, a speed reduction gear, a switch having first and second contacts and an operating cam rotated by said motor through said reduction gear, the thyratron having a control electrode and having an anode and a cathode in a circuit connected to said alternating-current terminals, a relay having a winding in series with the thyratron, a condenser shunting said winding, a pair of terminals for connection to a source of direct current, one connected to the cathode of said thyratron, the other connected to the first switch contact, a timing resistor connected at one end to said cathode, a timing condenser connected between said resistor and the second switch contact, and a connection between the thyratron control electrode and the junction of the condenser and resistor.

4. A timing system comprising in combination a pair of terminals for connection to a source of alternating current, a motor driven switch, a thyratron having a control electrode and having an anode and a cathode in a circuit connected to said alternating-current terminals, a device in series with the thyratron for carrying impulses of accurately fixed duration and interval, a pair of terminals for connection to source of direct current, a timing resistor and a timing condenser connected in series with said switch to said direct-current terminals, said timing resistor being included in a circuit between the cathode and control electrode of said thyratron.

5. A timing system comprising in combination a constant speed motor, a switch driven thereby having a pair .of contacts, a pair of terminals for connection to a source of alternating current, a translating device in which current pulses are to be produced, a thyratron having a cathode and an anode connected in series with said translating device to said alternating-current terminals and having a control electrode, timing resistance means connected in a circuit between the cathode and the control electrode of the thyratron, positive and negative terminals for connection to a source of direct current, and a timing condenser connected in series with the timing resistance means and the switch contacts between the direct-current tertminals, the connections of the timing resistance means being such that the cathode end thereof is more negative than the positive end thereof.

References Cited in the tile of this patent UNITED STATES PATENTS 2,525,969 Sparks Oct. 17, 1950 

